1. Field of the Invention
The present invention relates to a muffler for a small general-purpose engine, in which a noise reduction chamber is formed by a case having a pair of case halves coupled to each other through their flanges.
A muffler for a small general-purpose engine is disclosed in Japanese Utility Model Publication No. S55-10580, in which a noise reduction chamber is formed by a case having a pair of case halves coupled to each other through their flanges, and directly secured to an engine. In this muffler, one of the case halves having an inlet for introducing the exhaust gas from the engine at the upper portion, and the other case half having an exhaust gas outlet at the lower portion, are coupled to each other by seam welding at flanges of both the case halves to form the case. A vertically extending first guide member of a Ushaped cross section is provided in the case so that the exhaust gas introduced through the inlet is turned downward, and is turned upward by a vertically extending second guide member which is provided downstream of the first guide member and has a U-shaped cross section.
In such a muffler, the exhaust gas from the engine is guided downward by the first guide member immediately after the exhaust gas enters the muffler through the inlet, in a direction substantially perpendicular to the entering direction, and the exhaust gas is then guided upward by the second guide member. This structure causes a large flow resistance to the exhaust gas, restricting the flow of the exhaust gas and lowering the engine output. Providing a curved form of the first guide member, along which the exhaust gas entering the muffler is smoothly guided downward for avoiding this problem, has a drawback in that the muffler is increased in size.
Further, in such a muffler, it is difficult to sufficiently lower the noise level because the exhaust gas expands only once, when it enters the upper noise reducing space in the case from the second exhaust gas passage in the second guide member. Further, the relatively complicated structure of the exhaust gas passage in the muffler, and a seam welding for coupling two case halves, are disadvantageous in terms of cost as for a muffler for a small general-purpose engine.
A muffler of more simple construction and easier to manufacture than that of the above is disclosed in Japanese Utility Model Publication No. H2-27129. More specifically, the interior of the case of the muffler is divided by a partition plate into two chambers, and the case is formed by coupling flanges of the pair of case halves by edge folding, sandwiching a partition plate therebetween to form a muffler of simple construction for easy production, while maintaining noise reduction. However, a need for improvement still remains with regard to such a muffler for a small general-purpose engine, because the edge folding of the case halves and the partition plate for facilitating production may cause a leakage of the exhaust gas which lowers the noise reduction effect and may allow a seeping out of oil in the exhaust gas, depending upon the accuracy of coupling procedure.
An object of the present invention is solving the above problems, and providing a muffler for a small general-purpose engine having a simple structure and an excellent noise reducing effect, in which a pair of case halves are coupled to each other through their flanges to form a noise reduction chamber in the case.